Wow! the EAT 300B are very expensive....
I have tried the EML 300B/5U4G combo with TS BG/RP 6SN7GT, Treasure CV181Z and TS BG/RP 6F8G in my amplfiier and with all my different headphones. Since I am coming from years in the Solid State world and specifically Class A I am used to fast, tight but deep bass and very controlled sound. Out of the 3 combinations with the EML tues I liked the most the one with the TS BG/RP 6F8G becuase it gave me the biggest soundstage, best definition of sound, best bass and kept the sweetnes of the midrange. For the type of music I listen the most (Pop and Classic Rock) IMO was the best combination.
I have other tubes on my way to roll but so far this combination really sounds good to me. My headphones collection never sounded so good including using my Rudistor RP010B.
I have also tried other 5U4G tubes. I bought a pair of new Electro Harmonix while I was waiting for the EML. The EH are crap. The sound got really harsh and with no body. I got a pair of NOS RCA and Tungsol. The RCA have a good balanced sound but not as goos as the EML. The Tungsol have a lot of bass but becuase of that the sound is not a crisp and clean.
IMO if you are going to invest that much money in the EAT 300B you should go with the best rectifiers you can afford. If I was in your position would go with the EML and the Sophia as second choice.